1. Field of the Invention
This invention relates to a lever type hoist. To be more specific, this invention relates to a lever type hoist designed to prohibit hoisting of load when any load heavier than the approved rated load is hung on it. Moreover, this invention relates to a lever type hoist allowing continuous lowering of the load chain on the end side to which the lower hook is not connected, under the no-load condition. Furthermore, this invention relates to a lever type hoist which enables smooth positional adjustment of the lower hook with a small force.
2. Description of the Prior Art
Conventionally, either of the following methods was adopted to make a positional adjustment of the lower hook by moving it in the direction of height by pulling the load chain mounted on the load sieve in a lever type hoist under the no-load condition:
(1) Moving the drive shaft to the operating wheel side to release the connection between the pinion fixed to one end of the drive shaft concerned and the geared transmission system which transmits rotation to the load sieve and enable free rotation of the load sieve and pulling the load chain in the state of free rotation.
(2) Moving the presser drive member to the operating wheel side to separate it from the pressure receiving member to enable free rotation of the load sieve and pulling the load chain in the state of free rotation.
However, those methods presented problems as described hereunder and improvement of the methods was strongly desired.
Namely, in the method (1) above, the braking force applied at the time of free rotation to the load sieve disconnected from the drive shaft side diminished. For that reason, in case the connection between the drive shaft and the load sieve is released during the work, the load sieve gets in the state of free rotation, presenting a risk of accident with unexpected falling of baggage or loosening of tightened baggage. There was also a danger that, in the state where the connection between the drive shaft and the load sieve is released, the speed of moving the lower hook by pulling the load chain gets faster than the expectation of the worker, causing an unexpected accident to the worker. In addition, when lifting up or down the next baggage, it was necessary to move the drive shaft disconnected from the load sieve side at the time of free rotation to the geared transmission system side while turning it and engage the pinion fixed to one end of the drive shaft concerned with the geared transmission system.
In the method (2) above, if you make a positional adjustment of the lower hook in the direction of height under the no-load condition, the rotation of the load sieve becomes heavy, making it impossible to make the adjustments continuously with a small force. For that reason, each time when the rotation of the load sieve became heavy, it was necessary to repeat the troublesome operation of loosening the presser drive member by manipulating the operating lever. The inventor thoroughly investigated into the cause of heavy rotation of the load sieve and found that the presser drive member moved in the direction of separating from the pressure receiving member gets in contact with either the external cover of the operating lever or other components and that this contact frictional force prevents the free rotation of the load sieve.